An electrophotographic image forming apparatus uses a developing device having a casing and a developing roller rotatably supported thereto. On a surface of the developing roller, a thin layer of toner having a uniform thickness needs to be formed. To this effect, the developing device is provided with a thickness regulation blade configured to be in contact with the surface of the developing roller for flattening toner provided thereon.
There are two types of thickness regulation blades: “against-type” and “with-type.” Assuming that a thickness regulation blade has a base end fixed to the casing of the developing device and a distal end in contact with the surface of the developing roller, the thickness regulation blade is called as “against-type” when a direction from the base end toward the distal end is opposite to a rotation direction of the developing roller; and the thickness regulation blade is called as “with-type” when the direction from the base end toward the distal end is coincident with the rotation direction of the developing roller. There is also known a conventional thickness regulation blade having a portion provided with a regulating portion made of a rubber material, the portion being in contact with the surface of the developing roller.